1. Field of the Invention
The present invention relates generally to a recording apparatus. More particularly, the present invention relates to an improvement of a recording apparatus preferably employable not only for a facsimile unit, an electrophotographic copying unit, a printer or the like and a composite unit having functions derived from the foregoing units but also as an output unit for a work station.
2. Description of the Prior Art
Conventionally, recording apparatuses of the foregoing type are classified into two types, one of them being a so-called serial scanning type of recording apparatus including a recording head arranged to achieve recording therewith by scanning and the other one being a so-called full line type of recording apparatus including a recording head fixedly arranged across the maximum width of a recording sheet. Any one of the conventional recording apparatuses as mentioned above is constructed such that a recording medium such as a recording sheet or the like is conveyed by recirculatively driving a conveyance belt so that recording is performed on the recording medium by activating a recording head. The configuration of the surface of the conveyance belt and the width of the same have a significant effect on performances of the recording apparatus as will be described below.
Next, an item "configuration of surface of conveyance belt" and an item "width of conveyance belt" will item-wise be described below as to how the performances of the recording apparatus are affected by these items.
With respect to the item "configuration of surface of conveyance belt":
A recording process of the conventional recording apparatus can be practiced in various manners. In recent years, attention has been paid to a non-impact type recording process in consideration of the fact that noise is generated only to a negligibly small extent during each recording operation. In connection with the non-impact type recording process, it has been confirmed that an ink jet type recording process is very advantageously employable for the recording apparatus because it makes it possible to perform recording at a high speed, and moreover, any particular fixing step is not required for achieving the recording when so-called plain paper is used as a recording medium.
An image recording apparatus having the foregoing ink jet type recording process employed therefor is constructed such that a recording medium such as a paper, a synthetic resin sheet or the like (hereinafter referred to generally as a recording sheet) is conveyed to an image building station by driving, e.g., a conveyance belt so that an image is built on the recording sheet in the image building section. In the case that conveyance of the recording sheet is unstable, there arise malfunctions that the image is elongated or contracted and an optical concentration of the image fluctuates from location to location on the image, resulting in quality of the image being remarkably degraded. For this reason, it is an inevitable subject to be solved for the recording apparatus that the conveyance of the recording sheet is stabilized.
To facilitate understanding of the present invention, a typical, conventional ink jet type image recording apparatus will be described below with reference to FIG. 7.
In FIG. 7, reference numeral 301 designates a scanner section in which an original is optically read and the result derived from the optical reading is converted into an electrical signal. The electrical signal converted in the scanner section 301 is inputted into a recording head portion 305 of a printer section 302 as a drive signal. Recording sheets each serving as a recording medium are received in a sheet feeding portion 303 so that they are delivered toward a belt conveyance portion 304 one by one as desired. As each recording sheet is displaced below the recording head portion 305 by recirculatively driving the belt conveyance portion 304, an image is recorded on the recording sheet by activating the recording head portion 305, and thereafter the recording sheet is delivered to a tray 308 via a fixing/sheet discharging portion 307. In addition, reference numeral 306 designates a restoring cap portion which has a function for maintaining the recording head portion 305 in the operative state so that it is normally ready to perform recording.
A conveyance belt usually employed for the image recording apparatus is made of a band-shaped material such as a synthetic resin such as polyurethane or the like or an elastomeric material such as rubber or the like and prepared in the form of an endless belt of which opposite ends are joined to each other by fusing or a similar process. A certain magnitude of voltage is applied to the surface of the conveyance belt by activating a charger (not shown) to induce an electric charge thereon so that a recording sheet is attracted electrostatically on the conveyance belt and an image is recorded on the recording sheet by activating the recording head portion 305.
When the conveyance belt is prepared in the form of an endless belt in the above-described manner, it is difficult from the technical viewpoint that opposite ends of a band-shaped material are exactly joined to each other, resulting in a line-shaped joint portion (hereinafter referred to as a joint line) formed therebetween being unavoidably slightly recessed and raised at positions along the joint line. Once the recessed/raised spots are formed along the joint line in that way, the recording sheet fails to be reliably placed on the surface of the conveyance belt across the joint line. In addition, the gap between the recording sheet and the recording head varies from location to location along the joint line, resulting in quality of the image being undesirably degraded. Since a thickness of the conveyance belt as measured at the joint line is largely different from that at the other portions of the conveyance belt, when the joint line is positionally aligned with a driving roller as the conveyance belt is recirculatively driven, the speed of the conveyance belt varies, causing the image to be enlarged or contracted. In the case of a colored image, color overlapping or color dislocating occurs.
In the circumstances as mentioned above, in contrast with the foregoing type of conveyance belt made of a band-shaped material of which opposite ends are joined to each other to form a joint line, it has been hitherto required that the conveyance belt is prepared in the form of an endless belt from the beginning. To meet the foregoing requirement, however, it is unavoidable that the endless conveyance belt is made at a very expensive cost.
With respect to the item "width of conveyance belt":
Recording heads employable for the aforementioned ink jet type recording apparatus are classified into two types, one of them being a serial scanning type of recording head and the other one being a full line type of recording head. As far as a width of the conveyance belt is technically concerned, the full line type recording head is particularly advantageously employable for the recording apparatus.
Specifically, in the case that the serial scanning type recording head is employed for the recording apparatus, it is easy to perform recording only within the range defined by the width of a recording sheet by detecting the foremost end of the recording sheet as a carriage moves. In addition, the size or area of a blank space on the recording sheet can adequately be adjusted by properly controlling an interval from the time when the foremost end of the recording sheet is detected until the time when a recording operation is started. On the other hand, in the case that the full line type recording head including a number of nozzles in the transverse director is employed for the recording apparatus, it is fixedly mounted on the recording apparatus. Thus, if a recording sheet fails to be correctly aligned with the nozzles during a conveying operation, there arises a malfunction that characters or images are erroneously recorded at the positions located away from the foremost end of the recording sheet. At the same time, the size or area of a blank space on the recording sheet varies. When ink is ejected from all the nozzles of the serial scanning type recording head because of some trouble, there is no possibility that the interior of the recording apparatus is contaminated with the extra ink ejected from the nozzles because no ink is ejected therefrom at the position where the recording head moves beyond a home position. On the contrary, in the case that the full line type recording head including a number of nozzles in the transverse direction is employed for the recording apparatus, ink is ejected from all the nozzles at all the positions, causing the extra ink ejected therefrom to flow outside of the recording sheet and the conveyance belt. Thus, the interior of the recording apparatus is noticeably contaminated with the ink.
Any particular consideration has not hitherto been taken with respect to the relationship among a width of the conveyance belt, a length of the recording head including a number of nozzles in the transverse direction and a width of the recording sheet. Therefore, no satisfactory measure has been taken to obviate the malfunction that ink is erroneously ejected from the recording head, resulting in the interior of the recording apparatus being contaminated with the ejected ink.
With respect to the aforementioned conventional recording apparatus, it is very difficult from the technical viewpoint that the conveyance belt is made in the form of an endless belt from the beginning using a molding die so as to meet the requirement for making uniform the thickness of the conveyance belt along the full length of the latter. This leads to a problem that the conveyance belt is made at an expensive cost.
Another problem is that the interior of the recording apparatus is contaminated with extra ink when the ink is erroneously ejected from the recording head and then flows outside of the width of the conveyance belt.